diff --git a/src/shared/image_utils.js b/src/shared/image_utils.js
index ff8e124d4037f..d234190b5c811 100644
--- a/src/shared/image_utils.js
+++ b/src/shared/image_utils.js
@@ -14,6 +14,7 @@
  */
 
 import { FeatureTest, ImageKind } from "./util.js";
+import { MathClamp } from "./math_clamp.js";
 
 function convertToRGBA(params) {
   switch (params.kind) {
@@ -85,8 +86,12 @@ function convertRGBToRGBA({
   let i = 0;
   const len = width * height * 3;
   const byteOffset = src.byteOffset + srcPos;
-  // Use 32-bit reads for aligned sources; otherwise convert pixel by pixel.
-  const len32 = byteOffset % 4 === 0 ? Math.floor(len / 4) : 0;
+  // Bound aligned 32-bit reads to the source view.
+  // The scalar loops treat missing bytes as zeros.
+  const len32 =
+    byteOffset % 4 === 0
+      ? Math.floor(MathClamp(src.length - srcPos, 0, len) / 4)
+      : 0;
   const src32 =
     len32 > 0 ? new Uint32Array(src.buffer, byteOffset, len32) : null;
   const alphaMask = FeatureTest.isLittleEndian ? 0xff000000 : 0xff;
diff --git a/test/unit/image_utils_spec.js b/test/unit/image_utils_spec.js
index e008e17b48c7f..ca52061f65409 100644
--- a/test/unit/image_utils_spec.js
+++ b/test/unit/image_utils_spec.js
@@ -387,6 +387,51 @@ describe("image_utils", function () {
       expect(result.destPos).toEqual(5);
       expect(dest).toEqual(new Uint32Array([WHITE, BLACK, WHITE, BLACK, RED]));
     });
+
+    it("pads a truncated source with black for RGB_24BPP", function () {
+      const src = new Uint8Array(12).fill(255);
+      const dest = new Uint32Array(6).fill(WHITE);
+      const result = convertToRGBA({
+        src,
+        dest,
+        width: 3,
+        height: 2,
+        kind: ImageKind.RGB_24BPP,
+      });
+      expect(result).toEqual({ srcPos: 18, destPos: 6 });
+      expect(dest).toEqual(
+        new Uint32Array([WHITE, WHITE, WHITE, WHITE, BLACK, BLACK])
+      );
+    });
+
+    it("doesn't read past the end of the source for RGB_24BPP", function () {
+      const src = new Uint8Array(24).fill(255).subarray(0, 3);
+      const dest = new Uint32Array(4);
+      const result = convertToRGBA({
+        src,
+        dest,
+        width: 4,
+        height: 1,
+        kind: ImageKind.RGB_24BPP,
+      });
+      expect(result).toEqual({ srcPos: 12, destPos: 4 });
+      expect(dest).toEqual(new Uint32Array([WHITE, BLACK, BLACK, BLACK]));
+    });
+
+    it("handles a srcPos past the end of the source for RGB_24BPP", function () {
+      const src = new Uint8Array([255, 0, 0]);
+      const dest = new Uint32Array(2).fill(WHITE);
+      const result = convertToRGBA({
+        src,
+        dest,
+        srcPos: 6,
+        width: 2,
+        height: 1,
+        kind: ImageKind.RGB_24BPP,
+      });
+      expect(result).toEqual({ srcPos: 12, destPos: 2 });
+      expect(dest).toEqual(new Uint32Array([BLACK, BLACK]));
+    });
   });
 
   describe("GlobalImageCache decoded images", function () {